Respirator apparatus, sometimes called ventilator apparatus and interchangeably referred to thus herein, is widely used for administering artificial respiration or ventilatory assistance to a patient.
By way of general background, the following US patents disclose examples of such an apparatus, or of a pump and/or exhalation valve useful in such apparatus.
U.S. Pat. Nos. 4,807,616, 4,823,787 and 4,941,469 disclose a ventilator apparatus comprising a pump; a delivery conduit for delivering pressurized air to a patient; a relief valve preventing the pressure in the delivery conduit from rising above a predetermined peak value; a sensor for sensing the pressure in the delivery conduit; a storage device for storing the sensed peak pressure; and a comparator for continuously comparing the sensed pressure with the stored peak pressure and effective to energize the pump whenever the sensed pressure is below the stored peak pressure, and to deenergize the pump whenever the sensed pressure is generally equal to the stored peak pressure.
U.S. Pat. Nos. 6,073,630, 5,484,270 and 5,683,232 disclose a reciprocating pump particularly useful in ventilator apparatus, and includes a piston reciprocatable axially within a cylinder and dividing its interior into an inlet chamber and an outlet chamber, a wall fixed within the inlet chamber, and a drive housing fixed to the wall. The drive housing includes a motor, a rotor rotatable by the motor, a nut rotatable within the drive housing, and a screw threadedly coupled at one end to the nut and fixed at its opposite end to the piston. The piston is substantially unrestrained for axial and rotary movement such that forward and reverse rotation of the nut by the motor reciprocates the screw and the piston axially of the cylinder, and also permits the screw and the piston to rotate with respect to the cylinder to thereby even out wear between the piston and cylinder.
U.S. Pat. No. 6,283,122 discloses an exhalation assembly which includes a hollow flow-through body, having an air inlet port and an air outlet port. The inlet port is arranged to receive air for supplying to a patient, and the air outlet port is arranged to provide air to a patient. The device also includes an exhalation valve connected to the flow-through body, for facilitating selectable exhalation by a patient to whom air is being supplied. The exhalation valve includes an air exhalation port arranged to permit therethrough an outflow of exhaled air and a valve member arranged to selectably cover the exhalation port in response to a closure pressure applied thereto, and to uncover the exhalation port in response to an exhalation pressure applied thereto from the flow-through body through the exhalation port Also included is a pressure source for selectably applying a closure pressure to the valve member, wherein the valve member is operative to cover the exhalation port in response to at least a minimum closure pressure which has a smaller magnitude than an opposing exhalation pressure
Further by way of general background, U.S. Pat. No. 5,762,480 discloses a reciprocating machine that converts linear motion to rotary motion or vice-versa and is associated with a supply of working fluid, and includes rotational power apparatus having a rotational motion transfer member; a cylinder defining a longitudinal axis and having a first end at which are located working fluid input and output apparatus, and further having a second end; a piston located within the cylinder and arranged for linear, reciprocating travel along the longitudinal axis between the first and second ends; a connecting rod having a first end connected to the piston, and further having a second end portion; and linkage apparatus.